1. Field
The present invention relates to a compliant joint, and more particularly to a compliant joint used for a robot to prevent an injury to a human by collision with the robot.
2. Description of the Related Art
Generally, an industrial robot is widely used in various fields, for example, a production line, since it is capable of performing an assigned work accurately without a manual operation and supervision by a human. For instance, a robot used in an automobile industry performs a variety of work such as carrying and welding of an automobile body.
On the contrary, an intelligent service robot works interactively in an active space of humans. For instance, a robot cleaner detects a pollution level of a predetermined interior space and performs cleaning, thereby providing a necessary service for humans. However, such an intelligent service robot may collide with an obstacle unexpectedly during the work. In other words, the intelligent service robot bears a risk of accidental collision with a human. Therefore, for a harmonious interaction between the robot and the human, safety for humans has become an essential factor in designing the intelligent service robot.
The intelligent service robot will be referred to briefly as a ‘robot’ hereinafter. The robot has been designed to be flexible so as not to injure a human by collision. Such a technical solution is called ‘robot compliance.’ An active or a passive method can be used to endow the robot with the compliance. According to the active method, a controller detects a feedback signal of a force/torque sensor mounted to the robot and accordingly copes with a force or an impact applied from the outside. According to the passive method, mechanical elements such as springs and dampers are used to achieve the necessary safety.
The active method is limited in achieving the safety since controlling is performed in accordance with a feedback signal of a sensor. When using a vision sensor, for example, the vision sensor having low resolution is insufficient to promptly cope with a sudden external impact. Furthermore, if the signal of the sensor includes noise or if the external impact has an uncontrollable bandwidth, the active method is not effective.
However, the passive method using mechanical elements to absorb the external impact, rather than a special sensor, is capable of reacting to the impact instantly, with a low malfunction rate. Thus, development of a mechanism that maintains the safety of the human and the robot is required. In other words, the robot system needs to be designed and manufactured as intrinsically safe by achieving passive compliance.